A non-contacting shaft sealing device of this kind, hitherto, is generally constructed as shown in FIG. 12, in which helical dynamic pressure generating grooves 17 are formed parallel on a sealing end face 15a of rotary shaft side in its peripheral direction in order to generate a dynamic pressure (positive pressure) between the sealing end face 15a and the sealing end face of the seal case side at time of relative rotation of the both sealing end faces so that the generated pressure, the back pressure due to the fluid to be sealed acting on the sealing end face of seal case side, and the spring force pressing this sealing end face to the sealing end face 15a of rotary shaft side may be balanced, and the both sealing end faces are held in non-contacting state with a fluid film interposing therebetween.
By such helical dynamic pressure generating grooves 17, however, dynamic pressure is generated only when the rotary shaft or the sealing end face 15a is rotated in normal direction (direction A), but dynamic pressure is not generated between the both sealing end faces when rotated in reverse direction (anti-direction A). It could not be therefore applied in rotary machines that need to rotate the rotary shaft in both normal and reverse directions. Also, in rotary machines in which the rotary shaft thereof is rotated in one direction only, the degree of freedom of designing a device is very small because arrangement of installation of the sealing end face 15a with the dynamic pressure generating grooves 17 being formed thereon will naturally be determined by the rotating direction of the rotary shaft. Further, in a double seal and the like which is arranged side by side with different relative rotation of multiple sealing end faces 15a, an increase in cost results due to an increase in the type of parts since a seal ring formed with pressure generating grooves for rotation in normal direction and a seal ring formed with pressure generating grooves for rotation in reverse direction are necessary. In addition, the two types of seal rings can be mixed easily in handling and there is a possibility of making mistakes in assembly.